The present invention relates generally to electrostatographic printing machines for reproducing an original document on a copy sheet. In particularly, the printing machine of the present invention includes a developer module with at least two developer housings and means to alternately urge the photoreceptor belt into development engagement with one of the developer housing to develop the electrostatic latent image.
Generally, in the process of electrostatographic printing a photoconducting member is charged with substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive surface is exposed to a light image of an original document being reproduced. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After recording the electrostatic latent image on the photoconductive member, the latent image is developed by bringing a developer material comprising carrier granules having toner particles adhering triboelectrically thereto into contact therewith. The toner particles are attracted from the carrier granules to the electrostatic latent image to form a toner powder image which is subsequently transferred to a copy sheet and permanently affixed thereto in image configuration by pressure or heat. Alternatively, the electrostatic latent image may be developed with a liquid developer by loading, for example, a patterned, developer applicator roll having raised portions and recessed portions with liquid developer and bringing the applicator roll into contact with the photoreceptor so that the charge on the photoreceptor induces a charge in the liquid developer and pulls the liquid developer off the applicator roll in image configuration. This technique is described, for example, in U.S. Pat. No. 3,084,043 and U.S. Pat. No. 3,806,354.
Generally, each electrostatographic printing machine is provided with a single developer housing which produces a developed image of the color of the developer material included within the developer housing. Alternatively however, such as in the Xerox 6500 multi-color electrophotographic printing machine, a series of electrostatic latent images corresponding to a single color of the original document are produced. Successive partial color light images are employed to record each of the single color latent images. Each single color electrostatic latent image is developed with toner particles of a color complimentary to the color of the light image to form a subtractive system. Such a multi-color development system utilizes a plurality of developer rolls, each being adapted to furnish the appropriate color toner particles to the photoconductive member. The successive electrostatic latent images are developed with different color toner particles to produce a multi-color reproduction.
There is frequently a desire on the part of the user of such electrostatographic reproducing machines to provide the capability to copy documents in more than one color. Alternatively it is also desired by the users to provide portions of a reproduced document in one color and other portions, such as for highlight purposes, in a second color.